Ground source heat pump systems (“GHSP”) have been demonstrated as an efficient means of delivering heating and cooling for the purpose of space conditioning for all types of residential, commercial and public buildings. These systems operate by making use of the relatively stable temperature of the ground as either a heat sink or heat source. A ground heat exchange system using a water/glycol mixture as the heat transfer medium is used to exchange heat with the refrigerant cycle contained in the heat pump. In the summer period the refrigerant cycle is used to remove heat from the space and discharge this heat to the ground using the same heat transfer medium and ground heat exchange system. In the winter heating period the same cycle is used to extract heat from the ground and deliver it to the building space using the same refrigerant cycle.
Historically the cost and performance of these types of GSHP are dependent on the temperature of the ground which is the ultimate source or sink for the heat, and the design heating or cooling load that the heat pump needs to deliver to the space. Because the ground temperature can vary throughout the year, both the efficiency and the capacity of the heat pump can vary as a result of ground temperature changes. Based on the geographic location of the heat pump installation there can be a significant difference between the total amount of heat extracted from the ground during the heating months and the amount of heat rejected to the ground in the cooling months. In climates where there is a significant imbalance between the summer cooling requirements heat rejection and the winter heating requirements heat extraction, this imbalance results in both a performance penalty for the heat pump system and a larger and more expensive ground heat exchange system.
Systems that extract more heat from the ground than they reject are called heating dominated systems, and systems that reject more heat to the ground than they extract are called cooling dominated systems. While geography and general climate are a major influence on whether a system is heating and cooling dominated, other factors such as building occupancy, solar loading, and other internal loads can also affect the characteristic of the system and thus the size of the ground loop required to meet the loads.
As GSHP systems have become more widespread it has become common practice to serve multiple heat pumps from the same ground heat exchange system. Since the presence of the ground heat exchanger limits the potential land use above it, there is an economic benefit to limiting the size of the ground heat exchange system from both an installed cost and land use perspective